The present invention relates in general to DC-to-DC switching converter power supplies and more specifically to a converter circuit having substantially zero current in the switching transistor during turn-on and turn-off.
Many types of DC-to-DC converters are known in the art for converting a first DC voltage to a second, regulated DC voltage. Typically, the first DC voltage is converted to an AC voltage (or DC pulses) by a switching transistor or transistors. The AC voltage is then reconverted to a desired DC output voltage. Feedback of the output voltage is used to control the duty cycle or the frequency of the AC voltage produced by the transistor(s) so that the desired voltage regulation is achieved.
Switching converters are known to have a higher efficiency than other types of power supplies such as series-regulated power supplies. However, the efficiency of switching converters has been limited by losses in the switching transistor(s) during turn-on and turn-off, particularly in pulse-width modulated (PWM) converters since the switching transistor(s) must then simultaneously withstand high current and high voltage during both turn-on and turn-off. It is known that lossless switching is possible if the transistor is turned on or off at zero current.
Resonant converters use a variable frequency AC voltage for regulating the DC output voltage. In resonant converters it is possible to have either lossless turn-on or lossless turn-off, but not both. Furthermore, current flow in the transistor(s) of a resonant converter is high, thus putting a high current stress on the transistor(s). This requires costly transistors with a high current rating.
By increasing the switching frequency, a converter having smaller size, lower weight, lower cost and faster response can be obtained. However, the higher frequency switching aggravates transistor losses and degrades efficiency.
Accordingly, it is a principal object of the present invention to provide a DC-to-DC converter having substantially no switching losses in the switching transistor.
It is another object to provide a DC-to-DC converter with low current stress on the switching transistor.
It is a further object to provide a single-ended converter circuit adapted for lossless switching operation even at high frequencies.